The present invention relates generally to the electrical stimulation of bone for the promotion of osteogenesis or bone growth and relates specifically to the precise fixation of a cathode in the area where bone growth stimulation is desired.
U.S. Pat. No. 3,842,841 issued to Brighton, et al., Oct. 22, 1974 entitled "Constant Current Power Pack for Bone Healing and Method of Use," herein incorporated by reference, describes a system for promoting osteogenesis through the use of direct current of from five to twenty microamperes applied between a cathode inserted at the fracture or site of the bone defect and an anode applied to the skin, preferably by means of a surface electrode. The utilization of such a direct current from a cathode at the fracture site causes a higher than normal growth of bone cells in the vicinity of the cathode which is advantageous in expediting healing of a fracture or correction of a bone defect.
The above Brighton, et al. patent describes several types of cathodes which can be utilized to promote osteogenesis. One is a multi-strand stainless steel wire which is coated with an insulation, such as Teflon.RTM. having a bare portion which is implanted at the fracture site. In order to get this cathode to the fracture site, a small incision must be made in the skin and the underlying tissue and the cathode is then placed in the vicinity of the fracture. The other electrode is a rigid stainless steel cathode pin which is coated with an electrical insulation except for a bare region at the end of the pin. No incision is necessary and the pin is merely pushed or driven through the skin and soft tissues into the vicinity of the fracture site.
One difficulty with such electrodes is that by virtue of the fact that they placed through soft, flexible tissue layers into the fracture site, movement of the externally projecting portion of the cathode may move or dislodge the cathode from the most desirable position. Many times, there is provided an internal fixation device for holding bony tissue in a predetermined fashion until sufficient bone growth has occurred to hold the fractured bones in the required relative position. In this instance, surgery is required in order to permit implantation of the internal fixation device. However, utilization of such a device in the past, while permitting ease of placement of the cathode, has not resulted in position maintenance of cathodes at the fracture location.